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3.2 VR6 OEM+ intake manifold project.

305K views 629 replies 103 participants last post by  Ajfrassetto 
#1 ·
THE INTRODUCTION
Hey everybody..
Time to start the planning stages of a new intake manifold. Figured this would be the best forum for the brain dump.
My planned goal is to have an intake manifold that is modeled after the OEM manifold complete with the changeover valve and resonance port but with larger runners.
Lets try to keep the thread on that topic. I do not want a short runner nor the CVP.
The end result should be a manifold that fits the stock mounting points and plumbing that just kicks up the dimensions of the runner area to allow the engine to breath easier hopefully allowing a respectable gain up top while trying to minimize losses down low.

At this point, the all motor guys on the 3.2's are making +25% more power out of the engine than it came from the factory with and seeing rev limiters set 800+ RPM higher than stock.
I'm pretty sure the engineers didn't have this in mind when they designed the stock intake manifold. Below is a picture I took of a stock intake manifold I cut up to show the runner cross section. Yes, that is a water bottle cap sitting on the runner.. they are tiny!!!!

 
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#600 ·
The bog with a large plenum can be tuned out.

I wonder how much the secondary plenum volume really matters. Its really the effective wave length that changes the powerband. As long as that plenum can stay near atmospheric at wot it should be "big enough." I think a vacuum gauge/transducer on the secondary plenum may show something.
 
#601 ·
As long as that plenum can stay near atmospheric at wot it should be "big enough."


Agreed- but not sure it would be at 6-7k+


Who still has one of these cars and a willingness to buy a vac guage, poke a little hole, and go dyno?

Or..is there a digital vac gauge that has a hold peak reading option? Then street testing could be quick and easy.
 
#609 ·
would this work? https://www.amazon.com/Manometer-Differential-Backlight-Ventilation-Measurement/dp/B07K7HT3XJ

I have about 2-3 extra intake manifolds. I try to buy them for cheap from time to time when I see the for sale.

my goal was to one day cut them up for 3D scanning. Externally then Internally. Once scanned, use some CAD software to increase the sides just enough for everything to fit.

With 3D printing getting more popular, I figured it was only a matter of time before 3D scanning/printing was cheap enough to make a better OEM+ intake manifold.

I've been following this thread for years, and believe in all the work Josh (PowerDubs) has done. The last bottleneck is our Intake. Trying to increase airflow without sacrificing torque.

We want to increase our numbers, not just transition the power band from lower to higher (HPA CVP Intake).

I'm also still curious about the Bigger Throttle Body idea as well. Not sure if that was in this thread or a different one, and Josh can correct me if I'm wrong about this, but the bigger TB's dont open up 100% during WOT when you go with the bigger TB. I believe it has something to do with the software/tune and air flow sensor.

Also, if we did the vacuum testing, are there any other logs we want to capture (using VAGCOM).
 
#610 ·
When I did my custom bored 80mm TB, the car felt livelier until it would throw a CEL for adaptation limit reached.

I did not know Jeff Atwood at the time, so I sold it. He told me he could 100% fix the tune to make that TB work. Another thing I wish I did if things had worked out differently.

I don't know if it actually made any true power, or just that it was getting more air per the cars given throttle position unexpectedly. :p
 
#611 ·
Marv,

That is not only perfect because it has peak record function, but it also has a differential reading which is awesome!

You can BOTH plenums and if there is any vac at high rev WOT- you can see if it is just the lower plenum, or the higher plenum as well.

You can also see if those readings change when a bigger TB is installed. (removing a choke point).

I love this ****.
 
#613 ·
#615 ·
If cars maxed out at 0 PSI vac there would be no gain to air filters / boxes....and we already know they make a substantial measurable difference on the R32.

I get the idea that bottle necks move around- and some are worse than others- I just don't agree that Vdub designed the stock manifold plenums with 330-340-350 all motor bhp in mind at 7k+ rpm

I'll say- by all means Marv, get the 2lb +/- meter, tap and plug into each plenum and let us know what's what. No need to dyno since that box will record peak.

Just sat down and gave it a quick thought. I'm no mathematician, nor engine designer, but lets round atmo up to 15, round the engine to an easy 300 crank- so if everything being equal (which hardly ever happens)- that means 20bhp for every psi.

So 2psi should be enough...unless I am thinking about this wrong somehow now. You won't gain 40bhp on a manifold modification. I'd be very happy with a solid consistent 5whp if a plenum spacer is all it took.

The meter alone will tell you both plenums activity without need for modification or dyno. Heck- I might buy one to try on my motorcycle. I've been playing modifying that and dynoing.
 
#617 ·
Cool to see this thread get some activity once again. As some may know I have been playing with a 3.2 motor in my 24v mk4 gti. Basically a fwd r32 at this point (knuckles, steering rack etc are all r32 when its not in dragstrip mode). I have tested a fair bit of stuff already but I haven't bothered to mess with a stock intake manifold. I can confidently say I am making more than any stock motor 3.2 has made naturally aspirated and I find low rpm torque to be more than sufficient without the stock intake. I have considered playing around with the stock intake as I have a few laying around but its hard to knowingly take a step back. :) Yes in a heavy car low rpm tq is nice but my theory is if I am going full throttle at a low enough rpm where the stock intake would be a big advantage I am probably in the wrong gear to start with. It would be great to have the best of both worlds but the stock intake gives up too much up top for the gains down low. At least for me.

For those curious about power the car has already trapped over 112 mph in 90+ deg weather weighing 2650 lbs. Its a stock motor with cams, intake manifold, and a custom downpipe on AEM Infinity that I wired and tuned.
 
#622 ·
I find low rpm torque to be more than sufficient without the stock intake. I have considered playing around with the stock intake as I have a few laying around but its hard to knowingly take a step back. :) Yes in a heavy car low rpm tq is nice but my theory is if I am going full throttle at a low enough rpm where the stock intake would be a big advantage I am probably in the wrong gear to start with. It would be great to have the best of both worlds but the stock intake gives up too much up top for the gains down low. At least for me.

For those curious about power the car has already trapped over 112 mph in 90+ deg weather weighing 2650 lbs. Its a stock motor with cams, intake manifold, and a custom downpipe on AEM Infinity that I wired and tuned.
I'm a little confused by your statement. when you say stock intake, are you referring to the actual intake, or the intake manifold?
I'm assuming this is the same setup as in your signature block "12.44@110 Quickest (Only?) All Motor Mk4 - 3.2l of fun"

Do you have a thread of your build? I would be interested in seeing more of it. I'm not 100% sure how MK4/GTI compares to the R32 in weight difference. seems like you have an extra 400-500# lighter (at least) than some other light R32s.

Also, are you running stock cams?

If there's one thing I've learned, is that CVP or short runner intake manifolds just move the powerband (from low end power to high end power). I've been in some R32's with HPA's CVP and it just felt like a turd. My old cammed R32 ate him up. but if you're looking for all top end, higher trap, then you should be fine with that setup, esp with Cams, which really opens up mid range and top range, without sacrificing low end.


otherwise if you want to keep the low end as well, than all of us looking for ways to improve the current intake manifold is ideal. I ordered the gauge. hopefully I'll find some time this summer to get it all tested and post it here.
 
#619 ·
Better check the batteries in your calculator I think they might be bad, :)

Have your friend pm me a budget, how much power he wants, and a credit card number and I will build him a longblock just like it.
 
#625 ·
My point is complaining about low rpm power to me is like complaining about not enough power at part throttle - it just means you aren't driving the car properly. Downshift and get the rpm's up to where they need to be. Yes a heavy car like an r32 is always going to feel better with more tq down low but they sold MK4 Jetta wagons with 2l 8v motors that were plenty driveable. Its not like putting a short runner on a 3.2 turns it into this dog that is dangerous to drive. The solution is to just use the right gear. Just like the stock intake is a compromise - trading high rpm power for low rpm tq, so are most short runners. I would say I likely make the same tq down low as a completely stock r32 did and vastly more the higher you rev it.

I don't have a build thread but its a pretty basic setup. No I am not on stock cams. Don't really see the point of either stock cams or intake manifold when trying to make power na. I have been tempted to maybe try a stock intake manifold just to see the difference but pretty hard to take that step backwards. I am always trying to make more power not less.

Hopefully I will get out there sooner rather than later and get some new numbers for my sig :)
 
#626 ·
r32 intake manifold project




according to me, you missed some informations….in first thread, deal was achieve a decent engine bhp without trading torque @low end in all motor, because it could killed drivebability in mk4 plateform with 1580kgs!!!
today to make power on r32 engine,this is a money & time question: pistons oversized with high CR, headwork, cams with 280deg 12mm lift and you could get 100bhp with oem intake…..there is no interest in this formula without spending a lot of cash money.

Not trading torque and increase top bhp, this is the real and initialised project. alot of people make some decent bhp but….engine couldn't be used in daily :facepalm:
 
#628 ·
according to me, you missed some informations….in first thread, deal was achieve a decent engine bhp without trading torque @low end in all motor, because it could killed drivebability in mk4 plateform with 1580kgs!!!
today to make power on r32 engine,this is a money & time question: pistons oversized with high CR, headwork, cams with 280deg 12mm lift and you could get 100bhp with oem intake…..there is no interest in this formula without spending a lot of cash money.

Not trading torque and increase top bhp, this is the real and initialised project. alot of people make some decent bhp but….engine couldn't be used in daily :facepalm:

Engine couldnt be used in daily? Not sure what you mean by that. Because you make 200 ft/lbs of tq instead of 230 at 3300 rpms, that makes it impossible to drive as a daily? Thats like saying a honda is impossible to drive as a daily because it only makes 150 ft lbs of tq TOTAL, and 250 hp. :what:
 
#629 ·
Split plenum

I have been following this thread on and off for years and was thinking if splitting and isolating the bottom plenum into 2 chambers for the first and second 3 cylinders (1,2,3 and 4,5,6), increasing their volume, increasing the tb and pipping size from intake and center feeding that into the top plenum from the middle and behind. Would this be a viable solution to add HP.

Maybe even separating into 2 TB
 
#630 ·
I have been following this thread on and off for years and was thinking if splitting and isolating the bottom plenum into 2 chambers for the first and second 3 cylinders (1,2,3 and 4,5,6), increasing their volume, increasing the tb and pipping size from intake and center feeding that into the top plenum from the middle and behind. Would this be a viable solution to add HP.

Maybe even separating into 2 TB



ive seen in the honda world, couple guys run 2 throttle bodies, some even run 3. Although as i say that, they run into 1 big plenum, but no real gains over ITBs, or even 1 big throttle body. I personally run 1 very big plenum, with a 90 mm throttle body. The runners are external runners above the plenum and are equal length. There are some things that i would change, to make a little more power, but this style intake has worked really well.
 
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